Phase stability of $$\upbeta$$ -MoSi2−x prepared by the Na flux method against thermal, oxidative, and mechanical treatments

The single \(\upbeta\)-MoSi2 phase was prepared by the Na flux method and its stability against thermal, oxidative, and mechanical treatments was investigated. The X-ray diffraction results show that the single \(\upbeta\) phase is formed at 600 °C within 1 h using pre-mixed Mo and Si powders with a Si/Mo molar ratio of 2.00–2.25. By energy-dispersive X-ray spectroscopy, the produced powder is found to be Si-deficient with a Si/Mo molar ratio of 1.87–1.96. The differential thermal analysis shows that the \(\upbeta\) phase transforms into the \(\upalpha\)-MoSi2 phase at 815 °C at 10 K/min with the segregation of a small amount of Mo5Si3. The transformation heat is −5.5 kJ/mol and the activation energy calculated by the Kissinger method is 290 kJ/mol. Thermogravimetry reveals that the \(\upbeta\)-MoSi2−x powder oxidizes significantly at 400–600 °C via the pest oxidation mechanism while it is resistant to oxidation at 700 °C for 5 h similarly to the \(\upalpha\)-MoSi2 phase. At last, mechanical milling on the \(\upbeta\)-MoSi2−x powder with a planetary ball mill up to 216 h demonstrates that this powder is stable under a severe mechanical treatment.